The present invention relates generally to satellite positioning systems and, more particularly, to antennas used with satellite positioning systems.
Various methods for machine control using position information from satellite positioning systems, such as the Global Positioning System (GPS), are known. In such methods, one or more satellite positioning system antennas are typically disposed on a vehicle, such as an earth-moving machine. Then the position of the antennas is determined using well-known positioning techniques in order to determine and control the positioning of the vehicle or various components of the vehicle, such as the various components of an earthmoving machine that are used in earthmoving operations. For example, FIG. 1 shows one such one such earthmoving machine, an excavator, which is well known in the art. As shown in FIG. 1, excavators such as excavator 100 typically have a main body 101 with a vehicle operator cab 102. Attached to the main body 101 is arm 103, commonly referred to as a “boom”. Boom 103 is, in turn, attached to a second arm 104, commonly referred to as a “stick.” Stick 104 may be adapted to hold different attachments. Here, stick 104 is attached, illustratively, to a bucket 105 for use in excavation/digging. Bucket 105 typically has prongs 106 attached to the leading edge of the bucket 105 that are used to break through ground and other materials to be excavated. Body 101 is attached to a base which is supported by, illustratively, tracks 107 that allow the excavator to move over a variety of surfaces. One skilled in the art will recognize that other bases have also been designed to be fixed in a single location and, therefore, have no tracks. Alternatively, some bases have been designed with wheels (instead of tracks) which may be desirable in different applications. Regardless the type of base, body 101 is typically attached to the base in a way such that body 101 is capable of rotating 360 degrees while the base remains stationary. Thus, the boom, stick and bucket are movable for digging or other purposes to all points around the base within a certain radius. One skilled in the art will recognize the bucket 105 may be moved with a high degree of flexibility within that given radius. For example, boom 103 may be raised or lowered by lengthening or shortening hydraulic pistons 108, respectively. Similarly, stick 104 may be rotated about pivot point 109 to raise or lower bucket 105 by shortening or lengthening hydraulic piston 110, respectively. Finally, bucket 105 may be rotated about pivot point 111 into a cupped or an open position by either lengthening or shortening hydraulic piston 112.
Excavators, such as excavator 101 in FIG. 1, are useful for many applications. For example, excavators may be used in the digging of trenches, holes and foundations; demolition; general grading and landscaping; heavy lifting (e.g., lifting and placing pipes); river dredging; etc. Initially, the operation of such excavators was performed by skilled operators in conjunction with a ground crew, for example a crew of workers equipped with surveying instruments to ensure, for example, the correct dimensions of an illustrative foundation in the ground. This mode of operation continues to be in widespread use today. However, this mode of operation is time consuming and labor intensive.
In order to decrease the time and cost associated with earthmoving operations, there have been various attempts at automating the operation of excavators and other earthmoving machines. For example, in one method disclosed in U.S. Pat. No. 6,782,644 to Fujishima et al., a satellite-based navigation system, such as the well-known Global Positioning System (GPS) or the Global Orbiting Navigation Satellite System (GLONASS), is used to control an excavator by remote control. Other similar systems have also been used to precisely monitor the movement of excavators during earthmoving operations.
FIG. 2 shows a prior art excavator using satellite positioning to increase excavation accuracy. Specifically, antennas 201 and 202 are mounted on body 101 of excavator 100. Using well known positioning techniques, the location of each antenna may be ascertained with a predetermined level of accuracy. The highest accuracy may typically be achieved with differential or real time kinematic (RTK) satellite positioning which uses a base station to help reduce the errors associated with received signals from positioning satellites. Such differential/RTK methods for reducing these errors are well known. Using such methods, the position of antennas 201 and 202 may be determined with a high degree of horizontal accuracy (illustratively plus or minus 5 millimeters) and vertical accuracy (illustratively plus or minus 12-18 millimeters).
Determining the precise locations of antennas 201 and 202 allows accurate determination of the orientation of the body 101 of the excavator 100. For example, if one antenna is positioned lower than the other it would indicate that the body is tilted. Additionally, since the position of each antenna on the body of the excavator is known, determining the position of antenna 201 relative to the position of antenna 202 will provide an accurate measurement of the heading of body 101 of the excavator. Thus, using two antennas allows both tilt and heading measurements of the body 101. However, simply knowing the tilt and heading of the body 101 is not sufficient for high-precision excavation. Instead, the precise orientation of the bucket 105 and, more particularly, the precise position and orientation of the leading (or cutting) edge of the bucket must be known.
Prior attempts have relied on various methods for determining the position and orientation of the leading edge of the bucket to facilitate precise excavation. For example, in one such method, angle sensors have been placed on the boom, stick and bucket linkage. Such angle sensors are also referred to herein interchangeably as inclinometers. Thus, referring once again to FIG. 2, sensor 203 is placed on body 101, sensor 204 is mounted to boom 103, sensor 205 is mounted on stick 104, and sensor 206 is placed on bucket 105. These sensors are calibrated for a given position of the cutting edge and or prongs of the bucket 105. Thus, any angular movement of the sensor (i.e., movement of the associated portion) can be measured. The dimensions of the boom, stick and bucket are known, and the length from the positioning system antennas can be measured. Accordingly, for any angular change detected by sensors 203-206 in FIG. 2, the location of the cutting edge of bucket 105 can be geometrically calculated and excavation operations can be accurately performed in less time using fewer people than prior manual methods.
In another technique, satellite positioning antennas are mounted to the stick of an excavator. Such technique is described in copending U.S. patent application Ser. No. 11/108,013, filed Apr. 15, 2005, and titled Method and Apparatus for Satellite Positioning of Earth-Moving Equipment, which is incorporated by reference herein in its entirety. According to that technique, satellite inclinometers antennas are used to determine the position and orientation of the stick and, then by using geometric calculations with, for example, one or more angle sensors on the bucket, the precise location of a portion of an attachment of the excavator/backhoe, such as the prongs of a bucket, can be determined.